The present invention is directed to field of casting molten metal. More particularly, the present invention is directed to a dual pump system and method of bottom filling a casting.
Conventional mold-filling methods involve filling a sand mold from the top through a sprue hole. Such a technique can result in creation of eddy currents which produce defects in the casting. If the defect goes beneath the surface, or if the article is a precision casting, such eddy currents can require scrapping of the entire casting. In their earlier patent, U.S. Pat. No. 7,213,634 entitled Offset Molding Process, Applicants have described one method of providing a suitable solution for obviating these eddy currents by bottom-filling the mold. However, that process has limited applicability in larger molds. The present invention is directed to a pumping system and a method for bottom-filling large molds by utilizing twin pumps which empty two identical crucibles by switching between the two to provide a continuous flow of molten metal to prevent the early fill from taking a set before the mold fill operation is complete.
The system of the present invention comprises a) a reservoir filled with molten metal to a first depth; b) a first pump crucible partially submerged in the reservoir, the first pump crucible having a first check valve positioned in a passageway in a bottom wall of the first pump crucible such that the first pump crucible will fill with molten metal to a second depth equal to the first depth; c) a riser tube extending upwardly from the first pump crucible, a first check valve in a bottom end of the riser tube to prevent downward flow of molten metal in the riser tube; d) a horizontally extending runner interconnecting the riser tube with a fill port in the bottom-fill mold; e) a high pressure source of inert gas interconnected to the first pump crucible by a gas delivery system including piping, at least one flow valve and a pressure regulator; whereby opening the at least one flow valve permits the inert gas to force the molten metal in the first pump crucible up the riser tube through the horizontally extending runner into the mold through the fill port.
The system further comprises a second pump crucible partially submerged in the reservoir, the second pump crucible having a second check valve positioned in a passageway in a bottom wall of the second pump crucible such that the second pump crucible will fill with molten metal to a third depth equal to the first depth. The at least one flow valve comprises a control valve for each of the first and the second pump crucibles and control means to enable switching between the first and the second pump crucible.
More preferably, the system for pumping molten metal to bottom fill a mold, comprising includes a) a reservoir filled with molten metal to a first depth; b) a first pump crucible submerged in the reservoir, the first pump crucible having a first check valve positioned in a passageway in a bottom wall of the first pump crucible such that the first pump crucible will fill with molten metal to a second depth equal to the first depth; c) a first riser tube extending upwardly from the first pump crucible, a first check valve in a bottom end of the riser tube to prevent downward flow of molten metal in the first riser tube; d) a horizontally extending runner interconnecting the riser tube with a fill port in the mold; e) a second pump crucible submerged in the reservoir, the second pump crucible having a second check valve positioned in a passageway in a bottom wall of the second pump crucible such that the second pump crucible will fill with molten metal to a third depth equal to the first depth; e) second pump crucible submerged in the reservoir, the second pump crucible having a second check valve positioned in a passageway in a bottom wall of the second pump crucible such that the second pump crucible will fill with molten metal to the third depth equal to the first depth; f) a high pressure source of inert gas interconnected to the first pump crucible and to the second pump crucible by a gas delivery system including piping, a pressure regulator, two flow valves, one for each the first and the second pump crucible, and a controller to switch between the two flow valves; g) a second riser tube extending upwardly from the second pump crucible, a second check valve in a bottom end of the riser tube to prevent downward flow of molten metal in the second riser tube; whereby opening one of the flow valve permits the inert gas to force the molten metal in a respective pump crucible up the riser tube through the horizontally extending runner into the fill port and switching to the other flow valve provides continuous flow of molten metal to the horizontally extending runner. The high pressure source of inert gas is preferably a tank of nitrogen maintained at 3000 psi and the pressure regulator supplies pressurized gas to the molten metal crucibles at no greater than 20 psi. The crucibles are manufactured from graphite and the riser tubes from refractory, ceramic or graphite.
The first and second check valves have a float ball having a first diameter, an end of the first and second riser tube being spaced from an upper surface of the check valve by a distance less than the first diameter to ensure the float ball remains captive in its respective check valve. Each of the crucibles has a lid which is cast around its respective riser tube to ensure absence of pressure loss between the lid and the riser tube.
In addition, the present invention includes a method of bottom-filling a mold with molten metal comprising the steps of a) providing two graphite crucibles submerged in a reservoir of molten metal, each the crucible being in fluid communication with the reservoir through a check valve; b) subjecting an interior compartment of a first one of the two graphite crucibles to a pressure in a range of between 12 and 20 psi forcing the molten metal within the first crucible past a first check valve up a first vertically positioned riser tube into a horizontally extending runner, through a fill port into the mold; c) switching pressure application from the first crucible to the second one of the two graphite crucibles, venting the first crucible to atmosphere enabling the first crucible to refill, the pressure range of between 12 and 20 psi forcing the molten metal within the second crucible past a second check valve up a second vertically positioned riser tube into the horizontally extending runner through the fill port into the mold; d) switching pressure back and forth between the second and first crucibles as often as needed to complete the fill process; whereby flow of molten metal from the first and second crucibles occurs continuously until filling of the mold is completed.
Various other features, advantages, and characteristics of the present invention will become apparent after a reading of the following detailed description.